1. Field of the Invention
The present invention relates to a stereo camera and, particularly, to a stereo camera having a prism finder for synthesizing one picture by the one-half portions of photographing pictures of right and left lenses.
2. Description of the Prior Art
There are as a stereo camera having two photographing lenses aligned in parallel in one camera body, a reflex-type stereo camera which views the pictures of right and left photographing lenses separately by right and left pentaprisms and a rangefinder type stereo camera which views a photographing field by one range-finder type finder or a real image type finder.
The reflex-type stereo camera has an advantage that a user can view the actual photographing picture through photographing lenses, but the structure that the two finders are simultaneously viewed by two eyes is difficult to have easy operability from the structure that one finder is viewed by a single eye. Particularly, it is difficult to simultaneously view the two finders in a stereo camera in which the pitch between right and left finders exceeds a distance (about 63.5 mm is known) between two human eyes from being limited by the outer diameter of the lens and the size of the lens-mounting mechanism.
In the conventional stereo camera that the distance between the right and left lenses is fixed, non-overlapping areas are generated at the outside of the right and left pictures due to the difference of the photographing fields of the right and left lenses. There are disadvantages that the loss of the picture is large since it is necessary to mask the non-overlapping areas which do not obtain stereo effect at the time of mounting.
Accordingly, the inventor of the present invention has proposed a stereo camera in which a composite prism is provided to synthesize one picture by introducing the outer one-half portions (inner one-half portions of a film exposing surface) of the photographing fields of right and left photographing lenses, enabling the synthesized picture to be observed through one finder, wherein a mechanism for adjusting the distance between the optical axes of the lenses interlocked to a focal point adjusting mechanism is provided, so that the photographing fields of the right and left lenses at a focal distance are brought into agreement with each other at all times to suppress the loss of the picture (Japanese Patent Application No. 8-053476).
Since this stereo camera brings the photographing fields of the right and left lenses at the focal distance, the focal point can be adjusted while observing the sideward deviation of the image of the right and left one-half portions of the finder picture synthesized by the one-half portions of the right and left photographing fields, and there are no deviation of subject image of the right and left one-half areas of the finder picture. When the right and left one-half portions of the finder picture become one normal image, the subject is focused.
Referring to FIG. 19(a), a circular subject is shown, and referring to FIGS. 19(b), 19(c) and 19(d), the finder images of the stereo camera are shown. When the subject of FIG. 19(a) is positioned at the center of the finder picture, the subject that is in focus appears in a real shape as shown in FIG. 19(b). The subject that is farther than the focal point, appears being broadened as shown in FIG. 19(c). The subject that is nearer than the focal distance, appears being narrowed as shown in FIG. 19(d). The focal point can be adjusted while observing the sideward deviation of the finder image of the right and left one-half portions of the finder image.
However, there exists not almost the state that all the subject in the pictures are disposed at the focal distance in fact, and the subjects are frequently mixed at various distances. When the certain subject is focused, the subject of the closer distance in the same picture is photographed in the state that the inter-optical axis distance correcting amounts of the lenses might become insufficient with respect to the close range subject in the same pictures. Since the human visual senses have collimation for noting a close range subject, a stereo slide that the subjects of various distances are mixed is appreciated by a viewer, the close range subject is focused at the extremely close range to be observed unnaturally. In order to correct it, at the time of mounting, it is necessary to suitably mask the outer areas of the right and left pictures.
Therefore, in the case of photographing at a close distance or the case except the photographing at the close distance that other subject does not exist between the main subject and the lenses, it might effectively suppress the loss of the picture the stereo camera is so constituted that the ranges of the photographing fields of the right and left lenses are brought into agreement at the closer distance than the focal distance.
In FIG. 20, an exponential curve A shown by a broken line shows the inter-optical axis distance/focal point adjusting focuses of the principal point of the right and left lenses that the ranges of the photographing fields of the right and left lenses are brought into agreement at a focal distance at all times. The exponential curve A of the conditions that the focal distance of the lenses is 36 mm and the pitch between the right and left exposure surfaces is 66 mm is shown in FIG. 21.
Let it new be presumed that a piece of thin lens is employed and that:
Focal distance of the lens - - - f PA1 Distance from the subject to the principal point of the lens - - - L PA1 Distance from the focal point of the lens to the image-forming position - - - .DELTA.if.
Then, there holds .DELTA.if=f.sup.2 /(L-f) and, hence, the distance between the principal point of the lens to the surface of the film becomes f+.DELTA.if.
Moreover, if the pitch between the right and left exposing surfaces of the stereo camera is P.sub.1, the shifting amount S1 of the right and left lenses for bringing the right and left photographing ranges into agreement s given by. EQU S1=(P.sub.1 /2).times.(f+.DELTA.if)/(L+f+.DELTA.if).
That is, the right and left lenses may be moved in a direction to approach each other by a shifting amount S1 calculated from the above equation with a decrease in the distance L from the subject to the principal point of the lenses. The exponential curve A is the locus based on the above equation.
Referring to FIG. 21, a solid line B is a straight line for connecting the point of shifting the right and left lenses from the exponential curve A to the inside at an infinite remote focal position F.sub.I to the point of bringing the photographing fields of the right and left lenses into agreement with each other at the shortest distance focal position F.sub.S, and except the shortest distance focal position F.sub.S, the photographing fields of the right and left lenses are brought into agreement at the close range from the focal distance. When it is so constituted that the right and left lenses are moved along the line segment of more inner shifting amounts in the entire area of the solid line B or the focal point adjusting range, the remote or close distance feeling adapted to the real photographing state that other subject exists at close distance from the subject of the focal distance is obtained.
However, when the stereo camera for synthesizing the one finder picture by the outer one-half portions of the above-mentioned right and left photographing pictures mounts the linearly moving type inter-optical axis distance and focus adjusting mechanism, the right and left lenses are shifted further inside from the position that the ranges of the photographing fields are brought into agreement at the shortest distance focal position F.sub.S (in the case of the solid line) or all focal point range (in the case of more line segments of the inner shifting amount from the solid line B). Accordingly, the subject image at the focal distance is observed to be broadened as shown in FIG. 19(c) even if the subject image is focused. Therefore, it has a disadvantage that focusing at the subject while observing the deviation of the finder image becomes impossible.
It therefore becomes necessary to solve the above-mentioned technical problem, so that the right and left focal photographing pictures can be viewed through one finder, and to provide a stereo camera having inter-optical axis distance/focus adjusting mechanism of inter-optical axis distance correcting amount adapted to the real photographing condition and and enabling to accurately adjust the focus by the finder image. The object of the present invention therefore is to solve the above-mentioned technical problem.